Auto-focus printing below 1,1 {33 {0 magnification

ABSTRACT

Automatic focusing is achieved for magnification factors ranging from above 1 X through and below 1 X by a mechanism which positions the negative with respect to the lens for a given magnification. The lens is positioned with respect to the image plane to establish the desired magnification. The negative holder is linked to the lens via a cam and follower which is configured to automatically establish the proper negative to lens spacing to maintain the system in focus.

United States Patent [1 1 Swing a v Apr. 17, 1973 [54] AUTO-FOCUSPRINTING BELOW 1,1 MAGNIFICATION v v [75] Inventor: Charles E. Swing,Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, NY. 221 Filed: Sept. 13,1971 21 Appl.No.': 179,745

[52 use .Q ..355/58,'355/56 51 int; Cl; ..co3b 27/36 [58]Fieldofsearchn; ..355/56,58,59

[56] 1 References Cited I UNITED STATES PATENTS l,677,778 6/1928 Hunter"3355/59 1,986,693' 1/1935 Uher 1,399,347 12/1921 Jobke 2,430,25211/1947 Simmon etal .....355/58 2,568,762 9/1951 Rabinow.... ..355/583,213,748 10/1965 Durst ..355/58 Primary Examiner--John M/HoranAssistant Examiner-E. M. Bero Attorney-W. H. J. Kline et a1.

[ v ABSTRACT 1 Automatic focusing is achieved for magnification factorsranging from above 1X through and below 1X by a mechanism whichpositions the negative with respect to the lens for a givenmagnification. The lens is positioned with respect to the image plane toestablish the desired magnification. The negative holder is linked tothe lens via acam and follower which is configured to automaticallyestablish the proper negative to len's spacing to maintain the system infocus.

4 Claims, 2 Drawing Figures ATTORNL Y5 I PATENTEUAPR 1 71975 AUTO-FOCUSPRINTING ISELOW 1,1 X MAGNIFICATION BACKGROUND OF THE INVENTION Thecommercial printing of photographs from nega- 5 tives has manyrequirements for varying print sizes either from a single negative orfrom a series of negatives. In many instances the required magnificationfactors vary above and below unity. Once the system has been set for asharp focus, it is highly desirable to be able to maintain this focusautomatically as the system is changed for varying magnifications. Onthe other hand, it has long been known that it is difficult to maintainthe focus as the magnification factor is changed through the 1Xmagnification. This is due to the fact that the overall (conjugate)distance decreases as the magnification factor approaches 1X from above,but increases below l The kinematics to be accomplished by the 'cam andlinkage system in maintaining focus through the 1X magnification zoneare impractical and therefore effectively limit the auto-focuscapability to magnifications above or below 1X, but not both. The knownsystems capable of automatically maintaining focus above, through andbelow unity are very complex, expensive and, in some instances,-difficult to use and maintain. In effect the prior art systems operatesimultaneously, but independently, on the lens carriage and the negativeholder.

An example of the prior art mechanism which provides autofocuscapability is disclosed in US. Pat. No. 3,408,145 issued on Oct. 29, 1968 to Bermarr M. S. Walzberg entitled, Auto-Focus Camera and DiaphragmMeans Therefor. Walzbergs apparatus utilizes a fixed copy holder andadjustable lens andnegative holders. The distance between the lens andthe copy holder is controlled by a crank and linkage connectedtherebetween and pin-pivoted at both ends. The distance between the lensand copy holder is .controlled through the action of a crank, cam track,follower and arm linked therebetween. Thus this apparatusrequires twonon-linear control mechanisms. Further, such apparatus has inherentlylimited magnification capability because of the structure of its cam andcam track.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is a principalobject of this invention to provide improved photographic apparatuscapable of providing magnification factors extending above and belowunity while maintaining focus automatically.

Another object of this invention is to provide automatic-focusingphotographic apparatus which is rel'atively simple in construction andoperation.

A more specific object of this invention is to provide automatic-focusphotographic printing apparatus which extends throughunity-magnification and uses a singular cam and-linkage to maintain theautomatic focus.

Still another object of this invention is to provide automatic-focusphotographic printing apparatus wherein the automatic-focus capabilityis continuous rather than incremental.

The foregoing and other objects are accomplished according to one aspectof the invention wherein the printer operator changes the magnificationfactor by first varying the position of the magnifying lens with jectdistance) and between the lens 15 and the plane 13 (i.e., imagedistance) are:

respect to the image plane and the photographic paper. A cam and linkageconnects the negative holder to the lens in a manner which automaticallyvaries the negative to lens distance to maintain the sharp focus. Thecam and linkage operates solely to adjust the lens/negative distancebased upon the magnification factor and therefore is relatively simpleof design and construction.

DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic opticalrepresentation of photographic printing apparatus in which the presentinvention finds utility; and

FIG. 2 is a side view in section of automatic-focus photographicprinting apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT While the following descriptionrelates to photographic printing apparatus, it will be readily apparentto those skilled in the art that it is equally applicable to a camerasystem requiring automatic focusing capabiliti'es.

Referring now to FIG. 1, there is shown in diagrammatic form aphotographic system including a negative plane 11 and an object plane 13with a lens 15 interposed therebetween. Assuming a lens having a focallength f, to obtain a focused image at a magnification m, the properdistances along the optical axis 17 between the negative plane 11 andthe lenslS (i.e., ob-

print Object Distance f 1+ llm) Image Distance f l m).

Discounting the'hiatus of the lens 15, the conjugate distance, O.A.,between the negative plane 11 and the print plane 13 for a magnificationm, is given by the equation:

If we were to assume a lens having a focal length, f, of 4 inches, formagnification factors varying from' 4 down to 0.6, we would find thevarious relations between the magnification, object distance, imagedistance, and conjugate distance to be as given in thefollowing table:

TABLET Object Image Conjugate Magnification Distance Distance DistanceWe can note the following relations between the distances described bythe above equations. First, as the magnification factor decreases, thedistance between the film negative 11 and the lens 15 increases.Conversely as the magnification decreases, the distance between the lens15 and the print plane 13 decreases. The difficult factor is theconjugate distance, O.A., which, as can be seen from the above table,decreases as magnification approaches one from above and then increasesagain as the magnification diminishes below one. his this factor whichhas made it particularly difficult to develop auto-focus apparatus withfixed print or negative plane, since in relating the lens and thenegative to the print plane, or conversely the lens and the print planeto the negative plane, there is defined thereby a complex hyperbolicequation which is difficult to reduce to a mechanical configuration. Theprincipal difficulty with the equation occurs as the magnificationfactor approaches unity, where the cam angle becomes too steep forpractical application. In some instances at unity magnification, the camangle would be 90, an impossible system. According to the presentinvention there lies the recognition that there is a direct relationbetween the magnification desired and the image distance or the distancebetween the lens and the print plane 13. Since the image distance can beadjusted in a relatively simple fashion, rather than determining anequation that will relate the negative plane 11 to the print plane 13for a given magnification and first adjusting the negative or printplane, we instead first adjust the lens with respect to print plane 13for a given magnification. Then the negative 11 is positioned withrespect to the lens 15. It can be seen from the above table and thedefined equations that this function is relatively simple.

Referring next to FIG. 2, there is shown in detail printing apparatuswith an automatic focus capability according to the present invention. Anegative carriage 21 and a lens carriage 23 are supported on a commonguide bar 25. The tops of the negative carriage and the lens carriageare connected by a constant tension spring 27 to eliminate any play inthe apparatus. The printer frame 29 includes a cam groove 31. Integralwith the negative carriage 21 at the bottom thereof is a nest 33 in theform of a forked section extending down from the carriage. A bell crank35 is attached to and pivots on an arm 37 of the lens carriage 23. Thearm 39- of the bell crank 35 supports a cam follower bearing 41 whichrides in the cam groove 31. Another arm 43,0f the bell crank supports anegative carriage positioning bearing 45 which rides in the nest 33 ofthe negative carriage.

In the negative carriage 21 is the negative focal plane 47 which isadapted to support a film negative. In the lens carriage 23 is supporteda suitable lens array 49. The optical centerline 51 passes through thecenter of the negative plane 47, the lens array 49 and impinges on thecenter of the image or print plane 53.

In FIG. 2, it can be seen that the cam groove 31 gradually slopesdownwardly going from left to right until the knee 55 is reached, atwhich point the groove falls off rapidly. As will become more readilyapparent, the knee 55 represents the position of the cam followerbearing for unity magnification, with positions to the left of the kneeconforming to magnifications in'excess of unity and positions to theright of the knee being magnifications less than unity.

In operation, the lens carriage 23 is moved relative to the print plane53 to give a desired factor of magnification. Movement may beaccomplished by any known motive means such as a chain belt drive ormotor and drive screw. With reference to FIG..2, if the lens carriage ismoved from left to right, the'cam following bearing 41 tracking in thecam groove 31 will move gradually downwardly as it approaches the knee55 of the cam groove 31. The downward movement of the bearing 41 in thecam groove 31 causes the bell crank 35 to be pivoted counterclockwiseabout the arm 37 of the lens carriage. Pivoting of the bell crank 35 inturn causes the negative carriage positioning bearing 45 to move in thenest 33 to move the negative carriage 21 relatively away from the lenscarriage 23. Thus, while the conjugate distance will be decreasing theobject distance and the image distance will be changing in the properproportions to insure automatic focusing for a given magnification aboveunity.

The increasing separation between the negative carriage 21 and the lenscarriage 23 is gradual until the point where the cam following bearing41 reaches the knee 55 of the cam groove 31. At this point the camfollowing bearing 41 will move rapidly downwardly in the cam groove 31.The configuration of the cam groove 31 is such that movement of the camfollowing bearing 41 to the right of the knee 55 will cause theseparation between the lens carriage 23 and the negative carriage 21 toincrease more rapidly than the decrease in separation between the lenscarriage 23 and the print plane 53 so that the conjugate distance beginsto increase to maintain automatic focusing for a given magnificationbelow unity.

While the equations relating to FIG. 1 ignored the hiatus of the lensarray, the actual configuration of the cam groove 31 can be determinedin the following manner:

Let X abscissa of the cam follower bearing 41, which equals the distancefrom the cam follower bearing to the print plane 53;

Let Y ordinate of the cam follower bearing 41, which is the distancefrom the cam follower bearing to the end of the arm 37 of the lenscarriage; then Y= Sin (o:+0)R, where M magnification of the system,

E effective focal length of the lens array,

F 1 front focus of the lens array,

F back focus of the lens array,

L length of the lens array, and

k a constant, being the horizontal distance between the back of the backfocus of the lens array and the pivot point at the end of the arm 37 ofthe lens carriage 23,

R effective radial length of the arms 39,43 of bell crank 35;

0 angle between the arms 39,43 of the bell crank" 35; a angle betweenthe arm 43 of the bell crank 35 and the horizontal axis.

' The angles: is readily determinable since it is equal to With theconfiguration for the cam groove 31 as calculated above, it has beenfound that by positioning the lens carriage 23 the proper distance fromthe print plane 53 to obtain the desired magnification, the negativecarriage 21 is automatically positioned properly to maintain theapparatus in focus. The cam groove 31 configuration is relatively simplein form so that no undue stresses are placed on the apparatus,and it isrelatively easy to maintain the alignment of the apparatus.

Referring back to the simplified formulas set out in the discussion ofFIG. 1, it can be seen that the object distance, that is the distancebetween the lens and the negative, approaches f, the lens focal length,as the magnification approaches infinity. Therefore, the groove 31 ofthe cam of FIG. 2 flattens out as the magnification increases and theonly limitation on the maximum magnification available with theapparatus according to the present invention, is on the length of theprinter frame in which the cam groove is machined.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

I claim:

1. In photographic printing apparatus including a housing and a printplane, a negative holder and a magnifying lens of fixed focal lengthpositioned in a lens carriage in said housing between said print planeand said negative holder, an automatic focusing drive mechanismoperative to maintain said apparatus in focus for a continuous range ofmagnification varying from less than unity to substantially more thanunity, saic; mechanism comprising:

first linear positioning means coupled to said lens carriage andoperative to position said lens the required distance from said printplane to effect a given magnification;

second positioning means coupled to said negative holder;

' support means extending from said lens carriage;

a bell crank having first and second arms, said bell crank beingpivotallysupported by said support means;

bearing means supported on said first arm of said bell crank andconnected to said second positioning means to control the positionthereof;

cam groove means supported by said housing and cam follower meanssupported by said second arm of said bell crank and positioned to ridein said cam groove means whereby movement of said cam follower means in.said cam groove means upon movement of said lens by said firstpositioning means will cause rotation of said bell crank andcorresponding movement of said bearing means to control the relativeposition between said lens carriage and said negative holder for therequired distance to maintain focus or any selected magnification.

2. The invention according to claim 1 wherein the required distancebetween the negative holder and the lens is in substantial agreementwith the equation f l l/m), where f is equal to the focal length of thelens and m is the given magnification factor.

3. The apparatus of claim 2, wherein said second positioning meansincludes an arm extending from said negative holder, said arm having anest in the end thereof vertically oriented with respect to the opticalaxis of said lens and wherein said bearing means rides in said nest.

4. The apparatus of claim 3, wherein said cam groove means is configuredto be in substantial agreement with the equations:

Y=Sin (a+0) R, where I M magnification of the system;

E effective focal length of said magnifying lens;

F front focus of said magnifying lens;

F back focus of said magnifying lens;

L= length of said magnifying lens;

k a constant, being the horizontal distance between the back focus ofsaid magnifying lens and the pivot axis of said bell crank at the end ofsaid support extending from said lens carriage;

R radial length between the axis of said bearing means and the pivotaxis of said bell crank;

0 angle between said first and second arms of said bell crank;

a angle between said first arm of the bell crank and the horizontal axiswhich is equal to cos(b /R) where b may be calculated from the apparatusgeometry by subtracting from the horizontal distance between back focusand pivot axis of said bell crank, the difference between the effectivefocal length of said magnifying lens divided by the selectedmagnification and the horizontal distance between said negative holderand the vertical centerline of said nest.

1. In photographic printing apparatus including a housing and a printplane, a negative holder and a magnifying lens of fixed focal lengthpositioned in a lens carriage in said housing between said print planeand said negative holder, an automatic focusing drive mechanismoperative to maintain said apparatus in focus for a continuous range ofmagnification varying from less than unity to substantially more thanunity, said mechanism comprising: first linear positioning means coupledto said lens carriage and operative to position said lens the requireddistance from said print planE to effect a given magnification; secondpositioning means coupled to said negative holder; support meansextending from said lens carriage; a bell crank having first and secondarms, said bell crank being pivotally supported by said support means;bearing means supported on said first arm of said bell crank andconnected to said second positioning means to control the positionthereof; cam groove means supported by said housing and cam followermeans supported by said second arm of said bell crank and positioned toride in said cam groove means whereby movement of said cam followermeans in said cam groove means upon movement of said lens by said firstpositioning means will cause rotation of said bell crank andcorresponding movement of said bearing means to control the relativeposition between said lens carriage and said negative holder for therequired distance to maintain focus or any selected magnification. 2.The invention according to claim 1 wherein the required distance betweenthe negative holder and the lens is in substantial agreement with theequation f ( 1 + 1/m), where f is equal to the focal length of the lensand m is the given magnification factor.
 3. The apparatus of claim 2,wherein said second positioning means includes an arm extending fromsaid negative holder, said arm having a nest in the end thereofvertically oriented with respect to the optical axis of said lens andwherein said bearing means rides in said nest.
 4. The apparatus of claim3, wherein said cam groove means is configured to be in substantialagreement with the equations: X ME + F1 + L + F2 + k - cos ( Alpha +theta ) R and Y Sin ( Alpha + theta ) R, where M magnification of thesystem; E effective focal length of said magnifying lens; F1 front focusof said magnifying lens; F2 back focus of said magnifying lens; L lengthof said magnifying lens; k a constant, being the horizontal distancebetween the back focus of said magnifying lens and the pivot axis ofsaid bell crank at the end of said support extending from said lenscarriage; R radial length between the axis of said bearing means and thepivot axis of said bell crank; theta angle between said first and secondarms of said bell crank; Alpha angle between said first arm of the bellcrank and the horizontal axis which is equal to cos 1(b/R) where b maybe calculated from the apparatus geometry by subtracting from thehorizontal distance between back focus and pivot axis of said bellcrank, the difference between the effective focal length of saidmagnifying lens divided by the selected magnification and the horizontaldistance between said negative holder and the vertical centerline ofsaid nest.